Imaging apparatus and method and liquid toner therefor

ABSTRACT

Scuff resistance, abrasion resistance and peel resistance of a wide class of liquid toners may be improved by the addition of a minor amount of an additional material which, at the fusing temperature used for the toner, has a much lower viscosity, preferably several orders of magnitude lower, than the viscosity of the toner particles at the fusing temperature and which forms a separate phase from the toner particles when solidified. It is believed that such material, during the fusing process, migrates to the outer surface of the image. During cooling of the image after it is fused, the additional material forms a substantially separate phase resulting in a hard slippery coating of the additional material which protects the image from abrasion.

FIELD OF THE INVENTION

The present invention relates to a liquid toner and imaging method andapparatus using the liquid toner.

BACKGROUND OF THE INVENTION

Liquid toners have been in use for a great many years. In U.S. Pat. No.4,794,651, and in a number of other patents and publications based onthis patent, liquid toner having fibrous or tentacular toner particlesmade of various material was described.

There has been a need to provide a liquid toner, which when used to forman image on a substrate, forms a more abrasion resistant image thanthose formed by prior art liquid toners.

It is known in the printing art to add particles, for examplepolyethylene particles, to ink or to the surface of the substrate inorder to improve the abrasion resistance of the ink. Such particlesproject from the surface of the printed image and the image is moreresistant to abrasion from paper. However, abrasion resistance to aconforming eraser is increase by a much smaller amount, if at all.

It is also known in the art to coat an already printed image with anabrasion resistant coating.

SUMMARY OF THE INVENTION

The present invention seeks to provide, in one aspect thereof, animproved toner having greater abrasion resistance than prior art toners.

The present invention seeks to provide in a related aspect a method forproducing images using the new liquid toner.

It has been found that the scuff resistance, abrasion resistance andpeel resistance of a wide class of liquid toners may be improved by theaddition of a minor amount of an additional material which, at thefusing temperature used for the toner, has a much lower viscosity,preferably several orders of magnitude lower, than the viscosity of thetoner particles at the fusing temperature and which forms a separatephase from the toner particles when solidified.

It is believed that such material, during the fusing process, migratesto the outer surface of the image. During cooling of the image after itis fused, the additional material forms a substantially separate phaseresulting in a hard slippery coating of the additional material whichprotects the image from abrasion.

It has been found that the additional material may be added at almostany point during the toner manufacturing process, but that the effect ofthe material is most pronounced when the material is added during thefinal stage of the grinding of tire toner or when it is separatelyground and added as finely ground material to the toner.

There is thus provided, in accordance with a preferred embodiment of theinvention an image forming method comprising:

providing an image on a substrate, the image comprising toner particlesincluding a polymer material, preferably comprising one or more of anethylene copolymer, an ethylene terpolymer or an ionomer; an additionalmaterial, preferably comprising one or more of polyethylene, apolyethylene wax, a homopolymer and a low molecular weight ionomer,which additional material is solid at room temperature; and carrierliquid;

fusing the image to the substrate by heating the image to a fusingtemperature at which the toner particles soften to a first viscosity,

wherein the additional material has a second viscosity at the fusingtemperature which is at least ten times lower and preferably at leasttwo or three orders of magnitude lower than the first viscosity.

Preferably the toner particles are solvated by the carrier liquid at thefusing temperature whereby their viscosity is reduced to the firstviscosity. Preferably the additional material is solvated by the carrierliquid at the fusing temperature whereby its viscosity is reduced to thesecond viscosity.

Preferably, during fusing or subsequent cooling, the additional materialmigrates to the surface of the image away from the substrate. In apreferred embodiment of the invention, during cooling, at least aportion of the additional material forms a separate phase from the tonermaterial at said surface, whereby the additional material forms aabrasion resistant layer covering the toner material.

In a preferred embodiment of the invention, the additional material iscomprised in the toner particles. Alternatively or additionally theadditional material is in a finely divided form and is dispersed in thecarrier liquid separate from the toner particles.

In a preferred embodiment of the invention, the additional material isat least partially incompatible with the toner particles.

There is further provided in accordance with a preferred embodiment ofthe invention, a liquid toner adapted for fusing at a fusing temperaturecomprising:

toner particles comprising a polymer material, preferably incorporatingone or more of an ethylene copolymer, an ethylene terpolymer or anionomer, which has a first viscosity at the fusing temperature;

an additional material, preferably comprising one or more ofpolyethylene, a polyethylene wax, a homopolymer and a low molecularweight ionomer, which additional material is solid at room temperatureand has a second viscosity at the fusing temperature; and

carrier liquid,

the first viscosity being at least ten times, preferably more than 100or 1000 times, the second viscosity.

In a preferred embodiment of the toner, the polymer material is solvatedby the carrier liquid at the fusing temperature whereby its viscosity isreduced to the first viscosity. Preferably, the additional material issolvated by the carrier liquid at the fusing temperature whereby itsviscosity is reduced to the second viscosity.

In a preferred embodiment of the liquid toner, the additional materialis comprised in the toner particles. Alternatively or additionally, theadditional material is in a finely divided form and is dispersed in thecarrier liquid separate from the toner particles.

Preferably, the additional material is at least partially incompatiblewith the toner particles.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1 is a simplified sectional illustration of electrostatic imagingapparatus constructed and operative in accordance with a preferredembodiment of the present invention;

FIG. 2 is a simplified enlarged sectional illustration of the apparatusof FIG. 1;

FIG. 3A is a simplified, cross-sectional side view of an intermediatetransfer member, including a removable intermediate transfer blanketmounted or a drum, in accordance with a preferred embodiment of theinvention;

FIG. 3B is a partially cut-away top view of the intermediate transfermember of FIG. 3A;

FIGS. 4A and 4B are respective top and side views of an intermediatetransfer blanket in accordance with a preferred embodiment of theinvention;

FIG. 4C shows details of the layered construction of the intermediatetransfer blanket in accordance with a preferred embodiment of theinvention;

FIG. 4D is a cut-away expanded view of a securing mechanism on theintermediate transfer blanket of FIGS. 4A and 4B; and

FIG. 5 is a simplified cross-sectional illustration of a portion of anintermediate transfer member, including a removable intermediatetransfer blanket mounted on a drum in accordance with another preferredembodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to FIGS. 1 and 2 which illustrate a multicolorelectrostatic imaging system constructed and operative in accordancewith a preferred embodiment of the present invention. As seen in FIGS. 1and 2 there is provided an imaging sheet, preferably an organicphotoreceptor 12, typically mounted on a rotating drum 10. Drum 10 isrotated about its axis by a motor or the like (not shown), in thedirection of arrow 18, past charging apparatus 14, preferably acorotron, scorotron or roller charger or other suitable chargingapparatus known in the art and which is adapted to charge the surface ofsheet photoreceptor 12. The image to be reproduced is focused by animager 16 upon the charged surface 12 at least partially discharging thephotoconductor in the areas struck by light, thereby forming theelectrostatic latent image. Thus, the latent image normally includesimage areas at a first electrical potential and background areas atanother electrical potential.

Photoreceptor sheet 12 may use any suitable arrangement of layers ofmaterials as is known in the art, however, in the preferred embodimentof the photoreceptor sheet, certain of the layers are removed from theends of the sheet to facilitate its mounting on drum 10.

This preferred photoreceptor sheet and preferred methods of mounting iton drum 10 are described in a copending U.S. patent application ofBelinkov et al., IMAGING APPARATUS AND PHOTORECEPTOR THEREFOR, filedSep. 7, 1994, assigned Ser. No. 08/301,775, the disclosure of which isincorporated herein by reference. Alternatively, photoreceptor 12 may bedeposited on the drum 10 and may form a continuous surface. Furthermore,photoreceptor 12 may be a non-organic type photoconductor based, forexample, on a compound of Selenium.

Imaging apparatus 16 may be a modulated laser beam scanning apparatus,an optical focusing device for imaging a copy on a drum or other imagingapparatus such as is known in the art.

Also associated with drum 10 and photoreceptor sheet 12, in thepreferred embodiment of the invention, are a multicolor liquid developerspray assembly 20, a developing assembly 22, color specific cleaningblade assemblies 34, a background cleaning station 24, an electrifiedsqueegee 26, a background discharge device 28, an intermediate transfermember 30, cleaning apparatus 32, and, optionally, a neutralizing lampassembly 36.

Developing assembly 22 preferably includes a development roller 38.Development roller 38 is preferably spaced from photoreceptor 12 therebyforming a gap therebetween of typically 40 to 150 micrometers and ischarged to an electrical potential intermediate that of the image andbackground areas of the image. Development roller 38 is thus operative,when maintained at a suitable voltage, to apply an electric field to aiddevelopment of the latent electrostatic image.

Development roller 38 typically rotates in the same sense as drum 10 asindicated by arrow 40. This rotation provides for the surface of sheet12 and development roller 38 to have opposite velocities at the gapbetween them.

Multicolor liquid developer spray assembly 20, whose operation andstructure is described in detail in U.S. Pat. No. 5,117,263, thedisclosure of which is incorporated herein by reference, may be mountedon axis 42 to allow assembly 20 to be pivoted in such a manner that aspray of liquid toner containing electrically charged pigmented tonerparticles can be directed either onto a portion of the developmentroller 38, a portion of the photoreceptor 12 or directly into adevelopment region 44 between photoreceptor 12 and development roller38. Alternatively, assembly 20 may be fixed. Preferably, the spray isdirected onto a portion of the development roller 38.

Color specific cleaning blade assemblies 34 are operatively associatedwith developer roller 38 for separate removal of residual amounts ofeach colored toner remaining thereon after development. Each of bladeassemblies 34 is selectably brought into operative association withdeveloper roller 38 only when toner of a color corresponding thereto issupplied to development region 44 by spray assembly 20. The constructionand operation of cleaning blade assemblies is described in PCTPublication WO 90/14619 and in U.S. Pat. No. 5,289,238, the disclosuresof which are incorporated herein by reference.

Each cleaning blade assembly 34 includes a toner directing member 52which serves to direct the toner removed by the cleaning bladeassemblies 34 from the developer roller 38 to separate collectioncontainers 54, 56, 58, and 60, for each color to prevent contaminationof the various developers by mixing of the colors. The toner collectedby the collection containers is recycled to a corresponding tonerreservoir (55, 57, 59 and 61). A final toner directing member 62 alwaysengages the developer roller 38 and the toner collected thereat issupplied into collection container 64 and thereafter to reservoir 65 viaseparator 66 which is operative to separate relatively clean carrierliquid from the various colored toner particles. The separator 66 may betypically of the type described in U.S. Pat. No. 4,985,732, thedisclosure of which is incorporated herein by reference.

In a preferred embodiment of the invention, as described in U.S. Pat.No. 5,255,058, the disclosure of which is incorporated herein byreference, where the imaging speed is very high, a background cleaningstation 24 typically including a reverse roller 46 and a fluid sprayapparatus 48 is provided. Reverse roller 46 which rotates in a directionindicated by arrow 50 is electrically biased to a potential intermediatethat of the image and background areas of photoconductive drum 10, butdifferent from that of the development roller. Reverse roller 46 ispreferably spaced apart from photoreceptor sheet 12 thereby forming agap therebetween which is typically 40 to 150 micrometers.

Fluid spray apparatus 48 receives liquid toner from reservoir 65 viaconduit 88 and operates to provide a supply of preferably non-pigmentedcarrier liquid to the gap between sheet 12 and reverse roller 46. Theliquid supplied by fluid spray apparatus 48 replaces the liquid removedfrom drum 10 by development assembly 22 thus allowing the reverse roller46 to remove charged pigmented toner particles by electrophoresis fromthe background areas of the latent image. Excess fluid is removed fromreverse roller 46 by a liquid directing member 70 which continuouslyengages reverse roller 46 to collect excess liquid containing tonerparticles of various colors which is in turn supplied to reservoir 65via a collection container 64 and separator 66.

The apparatus embodied in reference numerals 46, 48, 50 and 70 is notrequired for low speed systems, but is preferably included in high speedsystems.

Preferably, an electrically biased squeegee roller 26 is urged againstthe surface of sheet 12 and is operative to remove liquid carrier fromthe background regions and to compact the image and remove liquidcarrier therefrom in the image regions. Squeegee roller 26 is preferablyformed of resilient slightly conductive polymeric material as is wellknown in the art, and is preferably charged to a potential of severalhundred to a few thousand volts with the same polarity as the polarityof the charge on the toner particles.

Discharge device 28 is operative to flood the sheet 12 with light whichdischarges the voltage remaining on sheet 12, mainly to reduceelectrical breakdown and improve transfer of the image to intermediatetransfer member 30. Operation of such a device in a write black systemis described in U.S. Pat. No. 5,280,326, the disclosure of which isincorporated herein by reference.

FIGS. 1 and 2 further show that multicolor toner spray assembly 20receives separate supplies of colored toner typically from fourdifferent reservoirs 55, 57, 59 and 61. FIG. 1 shows four differentcolored toner reservoirs 55, 57, 59 and 61 typically containing thecolors Yellow, Magenta, Cyan and, optionally, Black respectively. Pumps90, 92, 94 and 96 may be provided along respective supply conduits 98,101, 103 and 105 for providing a desired amount of pressure to feed thecolored toner to multicolor spray assembly 20. Alternatively, multicolortoner spray assembly 20, which is preferably a three level sprayassembly, receives supplies of colored toner from up to six differentreservoirs (not shown) which allows for custom colored tones in additionto the standard process colors.

It has been found that the scuff resistance, abrasion resistance andpeel resistance of a wide class of liquid toners may be improved by theaddition of a minor amount, between 2% and 20%, preferably between 4% to15%, most preferably about 10% (with respect to the solids content ofthe toner) of an additional material which, at the fusing temperatureused for the toner, has a much lower viscosity, preferably severalorders of magnitude lower, than the viscosity of the toner particles andwhich forms a separate phase from the toner particles when solidified.It is believed that such material, during the fusing process, migratesto the outer surface of the image. During cooling of the image after itis fused, the additional material forms a substantially separate phaseresulting in a hard slippery outer coating of the additional materialwhich protects the image from abrasion. While not believed to beabsolutely necessary for the invention, the additional materials whichhave been found useful are at least partially incompatible with thetoner particles.

It has been found that the additional material may be added at almostany point during the toner manufacturing process, but that the salutaryeffect of the additional material is most pronounced when it is addedduring the final stage of the grinding of the toner or when it isseparately ground and added as finely ground material to the finishedtoner and dispersed in the carrier liquid. Somewhat less than optimumresults are achieved when the additional material is added at thebeginning of the grinding process or during the plasticization of thetoner.

The preferred additional material is Micronised Polyethylene Wax, forexample ACumist A-12, ACumist B-12 and ACumist C-9 (Allied Signal,Inc.). Other useful materials are A-C 9A and A-C 1702 Homopolymers(Allied Signal), and AC-290, AC-293A and similar ionomers which are lowmolecular weight ethylene-based copolymers neutralized with metal saltsforming ionic clusters, manufactured by Allied Signal and sold under thetrade mark "AClyn."

One preferred method of forming a toner having improved abrasionresistance is the following:

1) Solubilizing 1400 grams of Nucrel 925 (ethylene copolymer by Dupont)and 1400 g of Isopar L (Exxon) are thoroughly mixed in an oil heatedRoss Double Planetary Mixer at least 24 RPM for 1.5 hours, with the oiltemperature at 130° C. 1200 g of preheated Isopar L is added and mixingis continued for an additional hour. The mixture is cooled to 45° C.,while stirring is continued over a period of several hours, to form aviscous material.

2) Milling and Grinding 762 grams of the result of the Solubilizing stepare ground in a 1S attritor (Union Process Inc. Akron Ohio), chargedwith 3/16" carbon steel balls at 250 RPM, together with 66.7 grams ofMogul L carbon black (Cabot), 6.7 grams of BT 583D (blue pigmentproduced by Cookson), 5 grams of aluminum tri stearate and an additional1459.6 grams of Isopar L for eight hours at 30° C.

3) Continuation of Grinding 34.5 grams of ACumist A-12 is added andgrinding is continued for an additional 4 hours. While 4 hours isbelieved to be the optimal grinding time for the added material, muchshorter grinding periods and adding the ACumist A-12 at the start ofstep 2 (or even at the start of step 1) also give substantially improvedabrasion resistance. The resulting particles are fibrous particleshaving a measured diameter in the range of 1-3 micrometers.

The resulting material is diluted with additional Isopar L and Marcol 82to give a working developer in which the dry solids portion is about1.7% and in which the overall ratio of Isopar L to Marcol is betweenabout 50:1 and 500:1, more preferably between about 100:1 and 200:1.Charge director as described in U.S. patent application Ser. No.07/915,291 (utilizing lecithin, BBP and ICIG3300B) and in WO 94/02887,in an amount equal to 40 mg/gm of solids, is added to charge the tonerparticles. Other charge directors and additional additives as are knownin the art may also be used.

Alternatively, ACumist A-12 or one of the other materials listed can bepre-ground to a particle size of 1 to 2 microns and added to tonerproduced according to the above method, to which the ACumist A-12 wasnot added during grinding.

Another additional material which has been found useful is theprecipitate formed when the B-12 or the A-12 material (60 grams) isheated and solubilized together with 30 grams of zinc stearate in 556grams Isopar L and then stirred while cooling to room temperature. Thismaterial may be added during the grinding step or separately.

The above described process produces a black toner. Cyan, magenta andyellow toners can be produced by using a different mix of materials forstep 2). For Cyan toner 822 g of the solubilized material, 21.33 gramseach of BT 583D and BT 788D pigments (Cookson), 1.73 grams of D1355DDpigment (BASF), 7.59 grams of aluminum tri stearate and 1426 grams ofIsopar L are used in step 2. For Magenta toner, 810 grams of solubilizedmaterial, 48.3 grams of Finess Red F2B, 6.81 grams of aluminumtri-stearate and 1434.2 grams of Isopar L are used in step 2. For yellowtoner, 810 grams of solubilized material, 49.1 grams of D1355DD pigment,6.9 grams of aluminum tri-stearate and 1423 grams of Isopar L are usedin step 2.

The additional materials described above also give improved abrasionresistance for liquid toner based on Bynell 2002 (ethylene terpolymer byDupont), Surlyn 8940 or 8920 (ionomers by Dupont) and Iotek 8030(ionomer by Iotek) and blends of these materials. The use of additionalmaterials having the characteristics described above is believed to haveapplicability to a wide range of toners which comprise polymer particlesand hydrocarbon carrier liquids.

Intermediate transfer member 30, an especially preferred embodiment ofwhich is described in detail below (in conjunction with FIGS. 3 and 4),may be any suitable intermediate transfer member having a multilayeredtransfer portion such as those described below or in U.S. Pat. Nos.5,089,856 or 5,047,808 the disclosures of which are incorporated hereinby reference. Member 30 is maintained at a suitable voltage andtemperature for electrostatic transfer of the image thereto from theimage bearing surface. Intermediate transfer member 30 is preferablyassociated with a pressure roller 71 for transfer and fusing of theimage onto a final substrate 72, such as paper, preferably by heat andpressure. For the especially preferred toner described above, an imagetemperature of about 95° C. at the inception of fusing is preferred.

Cleaning apparatus 32 is operative to scrub clean the surface ofphotoreceptor 12 and preferably includes a cleaning roller 74, a sprayer76 to spray a non-polar cleaning liquid to assist in the scrubbingprocess and a wiper blade 78 to complete the cleaning of thephotoconductive surface. Cleaning roller 74 which may be formed of anysynthetic resin known in the art for this purpose is driven in the samesense as drum 10 as indicated by arrow 80, such that the surface of theroller scrubs the surface of the photoreceptor. Any residual charge lefton the surface of photoreceptor sheet 12 may be removed by flooding thephotoconductive surface with light from optional neutralizing lampassembly 36, which may not be required in practice.

In accordance with a preferred embodiment of the invention, afterdeveloping each image in a given color, the single color image istransferred to intermediate transfer member 30. Subsequent images indifferent colors are sequentially transferred in alignment with theprevious image onto intermediate transfer member 30. When all of thedesired images have been transferred thereto, the complete multi-colorimage is transferred from transfer member 30 to substrate 72. Impressionroller 71 only produces operative engagement between intermediatetransfer member 30 and substrate 72 when transfer of the composite imageto substrate 72 takes place. Alternatively, each single color image isseparately transferred to the substrate via the intermediate transfermember. In this case, the substrate is fed through the machine once foreach color or is held on a platen and contacted with intermediatetransfer member 30 for composite image transfer. Alternatively, theintermediate transfer member is omitted and the developed single colorimages are transferred sequentially directly from drum 10 to substrate72.

FIGS. 3A, 3B and 4A-4D illustrate a preferred embodiment of intermediatetransfer member 30 in accordance with a preferred embodiment of theinvention. FIG. 3A shows an intermediate transfer blanket 100 mounted ona drum 102. Transfer blanket 100 (whose details are shown in FIGS. 4Cand 4D) comprises a preferably layered transfer portion 104 and amounting fitting 106.

As shown most clearly in FIG. 4C, transfer portion 104 comprises arelease layer 109 which is outermost on the blanket when it is mountedon drum 102. Underlying layer 109 is a conforming layer 111 preferablyof a soft elastomer, preferably of polyurethane and preferably having aShore A hardness of less than about 65, more preferably, less than about55, but preferably more than about 35. A suitable hardness value isbetween 45-55, preferably about 50. Underlying layer 111 is a conductivelayer 114 which overlays a thin barrier layer 115. Barrier layer 115overlays a blanket body 116 comprising a top layer 118, a compressiblelayer 120 and a fabric layer 122. Underlying the fabric layer is anadhesive layer 126 which is in contact with drum 102.

Drum 102 is preferably heated by an internal halogen lamp heater orother heater to aid transfer of the image to and from the release layer109 to a final substrate as is well known in the art. For the preferredliquid toner, the temperature at the surface of the intermediatetransfer member is preferably about 95° C. The degree of heating willdepend on the characteristics of the toner used in conjunction with theinvention.

As shown in FIGS. 4A, 4B and 4D, mounting fitting 106 comprises anelongate electrically conducting bar 108, for example, of a metal suchas aluminum formed with a series of L-shaped mounting legs 110 (in theform of finger-like extensions) which are also conducting, preferably ofthe same material as bar 108, and preferably formed integrallytherewith. In particular, bar 108 is formed with a slot into which theend of layered transfer portion 104 is inserted. Preferably, the end ofthe layered portion which is inserted into the mounting bar does nothave a release layer 109 or conforming layer 111, whereby conductinglayer 114 is exposed and is therefore in electrical contact with bar108. Alternatively, the bar 108 can be formed with sharp internalprojections which pierce the outer layers of the blanket and contact theconducting layer.

Optionally, each of the layers beneath the conducting layer 114 may bepartially conducting (for example, by the addition of conductive carbonblack or metal fibers) and the adhesive layer may be conductive, suchthat current also flows directly from the drum surface to the conductinglayer.

In one preferred embodiment of the invention, fitting 106 is formed of asingle sheet of metal, wherein the legs are partially cut from the metalwhich is bent into a U shape to form the slot into which the layeredportion is inserted. After insertion, the outer walls of the slot areforced against the layered portion to secure the layered portion in theslot. The partially cut out portion is bent to form the mounting legs.

In the preferred embodiment of the invention shown in FIGS. 1-3, drum102 is maintained at a potential suitable for transferring images to theintermediate transfer member, for example at 500 volts, which voltage isapplied, via mounting fitting 106 to conductive layer 114. Thus, thesource of transfer voltage is very near the outer surface of portion 104which allows for a lower transfer potential on the drum.

In a preferred embodiment of the invention, transfer portion 104 isfabricated by the following procedure:

1--The starting structure for blanket construction is a blanket body 116generally similar to that generally used for printing blankets. Onesuitable body is MCC-1129-02 manufactured and sold by Reeves SpA,Lodovicio (Milano), Italy. In a preferred embodiment of the invention,body 116 comprises a fabric layer 122, preferably of woven NOMEXmaterial and having a thickness of about 200 micrometers, a compressiblelayer 120, preferably comprising about 400 micrometers of saturatednitrile rubber loaded with carbon black to increase its thermalconductivity. Layer 120 preferably contains small voids (about 40-60% byvolume) and a top layer 118 preferably comprised of the same material asthe compressible layer, but without voids. Layer 109 is preferably about100 micrometers thick. The blanket body is produced by manufacturingmethods as are generally used for the production of offset printingblankets for ink offset printing.

Blanket body 116 is preferably sized to a relatively exact thickness byabrading portions of the surface of top layer 118. A preferred thicknessfor the finished body 116 is about 700 micrometers, although otherthicknesses are useful, depending on the geometry of the printing systemin which it is used and the exact materials used in the blanket body.

2--The fabric side of blanket body 116 is preferably coated with a 30micrometer thick coating of silicone based adhesive (preferably, Type D66 manufactured by Dow Corning). The adhesive is covered with a sheet ofmylar coated with a fluorosilicone material, such as DP 5648 ReleasePaper (one side coat) distributed by H. P. Smith Inc., Bedford Park,Ill. This adhesive is characterized by its good bond to the surface ofdrum 102 and is resistant to the carrier liquid used in the liquidtoner. The blanket may be removed from the drum, when its replacement isdesired, by cutting the blanket along the edge of fitting 106 andremoving the blanket and fitting.

An adhesive is used to assure good thermal contact between the back ofthe blanket and the drum on which it is mounted. A silicone adhesive isused since adhesives normally used in attachment of blankets deteriorateunder the heat which is generated in the underlying drum in thepreferred apparatus. While the temperature of the drum varies, dependingon the thermal resistance of the blanket and the desired surfacetemperature of the blanket (which in turn depends on the toner used inthe process and the details of transfer of the toner to the finalsubstrate), the drum temperature may reach 80° C., 100° C., 120° C. or150° C. or more.

3--Top layer 118 is preferably coated with a sub-micron layer of primerbefore being coated with additional layers.

A preferred primer is Dow Corning 1205 Prime Coat. The type of primerdepends on the properties of the top layer and of the conductive layer.Preferably, 0.3 micron of primer is coated onto a clean top layer with aNo. 0 bar in a wire coating apparatus and is allowed to dry beforeapplying the conductive layer.

4--Since blanket body 116 may contain materials such as anti-oxidants,anti-ozonants or other additives which may migrate through the upperlayers of the blanket, for example as a gas, when the blanket is heatedduring the imaging process and/or in the presence of carrier liquid suchas Isopar L, barrier layer 115 is preferably coated onto top layer 116.This barrier layer should be substantially impervious to such materialsin the blanket body which may migrate and/or to the carrier liquid whichis used.

If this layer is omitted, under certain circumstances the additivematerials can cause deterioration of the photoreceptor. In particular,it was found that the imaging process may become humidity dependent.

In a preferred embodiment of the invention, a 4-11 micrometer layer ofpolyvinyl alcohol (88% hydrolyzed) is coated onto the primer layercovering top layer 118.

Polyvinyl alcohol, 88% hydrolyzed, having an average molecular weightpreferably between 85,000 and 145,000 (Aldrich Chemical Co. Inc.,Milwaukee, Wis.) is dissolved in water at 90° C. by continuouslystirring the mixture in a reflux system for 30 minutes. After 30minutes, a quantity of ethanol equal to twice the quantity of water isadded to the solution, the resulting polyvinyl alcohol concentrationbeing preferably less than 10%. Higher concentration solutions can beused; however, they give a more viscous solution which is hard to spreadevenly.

The solution is deposited on layer 118 of body 116 using a fine wire rodor knife inclined at 30-45° to the direction of movement of the knife orbody. The solvent is evaporated either by drying at room temperature orby blowing hot air on the layer.

One or more coating passes are employed to give the required thickness.

Too thin a layer will result in some transfer of material from body 116,which has been correlated with "clumping" or agglomeration of the tonerparticles in the liquid toner. This is believed to be caused byphotoreceptor deterioration. While four micrometers of material appearsto be sufficient to avoid leaching, a somewhat larger thickness, forexample, 6 micrometers, is preferably used.

Other barrier materials and other thicknesses may be used depending onthe carrier liquid used for the toner or the gasses released by body116. Other materials may require lesser or greater toner thicknessdepending on their resistance to the carrier liquid or the gassesreleased by body 116. Alternatively, if body 116 is resistant toleaching by the carrier liquid or does not contain materials which arereleased (especially when body 116 is heated), layer 115 may be omitted.

Polyvinyl alcohol is a thermoplastic crystalline material having amelting point which is higher than the temperature of the blanket duringoperation. Polyvinyl alcohol is also believed to form a layer which isimpervious to gasses and to the hydrocarbon carrier liquid used in theliquid toner.

Conductive layer 114 is preferably formed of acrylic rubber loaded withconductive carbon black. In a preferred embodiment of the invention,only 2-3 micrometers of conductive coating are required. The conductivelayer is formed by first compounding 300 grams of Hytemp 4051EP (B. F.Goodrich) with 6 grams of Hytemp NPC 50 and 9 grams of sodium stearatein a two-roll mill for 20 minutes; and then dissolving 150 grams of thecompounded material in 2000 grams of methyl ethyl ketone (MEK) bystirring for 12 hours at room temperature.

40 grams of conductive carbon black, such as, for example, Printex XE2(Degussa) are added to the solution and the mixture is ground in a 01attritor (Union Process) loaded with 3/16" steel balls. Grindingproceeds at 10° C. for 4 hours after which time the material is dilutedby the addition of MEK to a concentration of 7.5-8% solids anddischarged from the grinder in the form of a conductive lacquer.

The blanket (after step 3 or step 4) is overcoated with about 3micrometers of the conductive lacquer (three passes using a No. 0 rod)and allowed to dry for 5 minutes at room temperature.

An additional coating of primer is added over the conductive lacquer(except for the portion which is to be inserted into bar 108) before thesoft elastomeric conforming layer is applied.

The resistance of the conductive layer should preferably be more thanabout 20 kohms/square and preferably less than about 50 kohm/square.This value will depend on the resistivity of the layers above theconducting layer and on the aspect ratio of the blanket. In general, theresistance should be low enough so that the current flowing on theconducting layer (to supply leakage current through the overlyinglayers) should not cause a substantial variation of voltage along thesurface of the blanket. The resistance of the conducting layer and, moreimportantly, the resistance of the overlying layers control the currentflowing through the overlying layers. Generally speaking, the conductivelayer has a relatively low resistance and resistivity, the conforminglayer (layer 111) has a higher resistivity and the overlying releaselayer (layer 109) has a still higher resistivity.

6--One kg of pre-filtered Fomrez-50 Polyester resin (Hagalil Company,Ashdod, Israel) is dehydrated and degassed under vacuum at 60° C. 600grams of the degassed material is mixed with 1.4 grams ofdi-butyl-tin-diluarate (Aldrich) and degassed at room temperature for 2hours. 30 grams of the resulting material, 3.15 grams of RTV Silicone118 (General Electric), 4.5 grams of Polyurethane cross-linker, DESMODUR44V20 (Bayer) and are stirred together. A 100 micrometer layer of thematerial is coated over the primed conductive layer using a No. 3 wirerod with several passes under clean conditions, preferably, class 100conditions. The coating is cured for two hours at room temperature undera clean hood to form a polyurethane layer.

Layer 111 which is thus formed should have a resistance of the order ofabout 10⁹ ohm-cm, good thermal stability at the working temperature ofthe blanket, which is preferably about 100° C. or less.

The function of the conforming layer is to provide good conformation ofthe blanket to the image forming surface (and the image on the imageforming surface) at the low pressures used in transfer of the image fromthe image forming surface to the blanket. The layer should have a ShoreA hardness preferably of between 25 or 30 and 65, more preferably about50. While a thickness of 100 micrometers is preferred, otherthicknesses, between 50 micrometers and 300 micrometers can be used,with 75 to 125 micrometers being preferred.

7--12 grams of RTV silicone 236 (Dow Corning) release material dilutedwith 2 grams of Isopar L (Exxon) and 0.72 grams of Syl-off 297 (DowCorning) are mixed together. A wire rod (bar No. 1) coating system isused, with five or six passes, under clean conditions to achieve an 8micrometer release layer thickness. The material is cured at 140° C. fortwo hours. The cured release material has a resistivity of approximately10¹⁴ to 10¹⁵ ohm-cm.

In order to mount blanket 100 on drum 102, mounting legs 110 areinserted into a plurality of mounting holes 130 formed in drum 102,preferably without removing the mylar sheet from the adhesive layer (theback of the blanket). As can be seen most clearly in FIGS. 3A, 3B and4D, mounting legs 110 each have a tip portion 132 and a back portion134. Tips 132 are inserted into slots formed in the far sidewalls ofmounting holes 130 and the back portion 134 rests against the oppositesidewall of the hole. In this way the end of the blanket is accuratelypositioned. The edge of the mylar sheet closest to the legs is removedand the remainder of the mylar sheet is progressively removed whilemaking sure that the successive portions of the blanket which are thusattached to the drum by the adhesive lie flat against the drum.

FIG. 5 shows an alternative, preferred embodiment of the invention inwhich somewhat different shaped holes 130' are used. In this embodimentthe back portion 134 rests against a protrusion 150 formed on one sideof the hole while a surface 154 of leg 110 rests against the bottom 156of a protrusion formed on the other side of the hole.

While the preferred electrical connection between the conductive layerand the mounting bar is preferably achieved by removing (or not forming)the layers which overlay an end portion of the conductive layer andpiercing the overlying layers, for example, by crimping and/or piercingthe mounting bar, for example, at points marked 160 in FIG. 4D. Crimpingcan also be used to hold the blanket in the mounting bar.

While the adhesive layer preferably covers the back of the blanket,alternatively the adhesive layer may cover only a portion of the backsuch as the edge farthest away from the bracket (the trailing edge ofthe blanket); or may, for some embodiments of the invention and undercertain circumstances, be omitted.

It should be understood that the invention is not limited to thespecific type of image forming system or transfer system used. Theinvention is also useful in systems, such as those using other types ofintermediate transfer members such as belt or continuous coated drumtype transfer members and also for imaging systems which use directtransfer of the image (for example from an imaging surface) to the finalsubstrate and which include a fuser for fusing the image to thesubstrate. Such systems are very well known in the art.

The specific details given above for the image forming system areincluded as part of a best mode of carrying out the invention. However,many aspects of the invention are applicable to a wide range of systemsas known in the art for electrophotographic printing and copying.

It will be appreciated by persons skilled in the art that the presentinvention is not limited by the description and example providedhereinabove. Rather, the scope of this invention is defined only by theclaims which follow:

We claim:
 1. An image forming method comprising:providing an image on asubstrate, the image comprising toner particles including a major amountof a polymer material, an additional material which is solid at roomtemperature and carrier liquid; fusing the image to the substrate byheating the image to a fusing temperature at which the toner particlessoften to a first viscosity; and cooling the image after fusing, whereinthe additional material has a second viscosity at the fusing temperaturewhich is at least ten times lower than the first viscosity.
 2. A methodaccording to claim 1 wherein the toner particles are solvated by thecarrier liquid at the fusing temperature whereby their viscosity isreduced to the first viscosity.
 3. A method according to claim 1 whereinthe additional material is solvated by the carrier liquid at the fusingtemperature whereby its viscosity is reduced to the second viscosity. 4.A method according to claim 1 wherein, during fusing or subsequentcooling, at least a portion of the additional material migrates to thesurface of the image away from the substrate.
 5. A method according toclaim 4 wherein, during cooling, at least a portion of the additionalmaterial forms a separate phase from the toner material at said surface.6. A method according to claim 1 wherein, after cooling, the additionalmaterial forms an abrasion resistant layer covering the toner material.7. A method according to claim 1 wherein the first viscosity is at least100 times the second viscosity.
 8. A method according to claim 1 whereinthe first viscosity is at least 100 times the second viscosity.
 9. Amethod according to claim 1 wherein the additional material comprises apolyethylene.
 10. A method according to claim 1 wherein the additionalmaterial comprises a polyethylene wax.
 11. A method according to claim 1wherein the additional material comprises a homopolymer.
 12. A methodaccording to claim 1 wherein the additional material comprises a lowmolecular weight ionomer.
 13. A method according to claim 9 wherein theadditional material further comprises zinc stearate.
 14. A methodaccording to claim 1 wherein the additional material is comprised in thetoner particles.
 15. A method according to claim 1 wherein theadditional material is in a finely divided form and is dispersed in thecarrier liquid separate from the toner particles.
 16. A method accordingto claim 1 wherein the polymer material comprises an ethyleneterpolymer.
 17. A method according to claim 1 wherein the polymermaterial comprises an ionomer.
 18. A method according to claim 1 whereinthe polymer material comprises an ethylene copolymer.
 19. A methodaccording to claim 1 wherein the additional material is at leastpartially incompatible with the toner particles.
 20. A liquid toneradapted for fusing at a fusing temperature comprising:toner particlescomprising a polymer material which has a first viscosity at the fusingtemperature; an additional material which is solid at room temperatureand has a second viscosity at the fusing in temperature; and carrierliquid, the first viscosity being at least ten times the secondviscosity.
 21. A liquid toner according to claim 20 wherein the polymermaterial is solvated by the carriers liquid at the fusing temperaturewhereby its viscosity is reduced to the first viscosity.
 22. A liquidtoner according to claim 20 wherein the additional material is solvatedby the carrier liquid at the fusing temperature whereby its viscosity isreduced to the second viscosity.
 23. A liquid toner according to claim20 wherein the first viscosity is at at 100 times the second viscosity.24. A liquid toner according to claim 23 wherein the first viscosity isat least three orders of magnitude greater than the second viscosity.25. A liquid toner according to claim 20 wherein additional materialcomprises a polyethylene.
 26. A liquid toner according claim 25 whereinthe additional material comprises a polyethylene wax.
 27. A liquid toneraccording to claim 20 wherein the additional material comprises ahomopolymer.
 28. A liquid toner according to claim 20 wherein theadditional material comprises a low molecular weight ionomer.
 29. Aliquid toner according to claim 25 wherein the additional materialfurther comprises zinc stearate.
 30. A liquid toner according to claim20 wherein the additional material is comprised in the toner particles.31. A liquid toner according to claim 20 wherein the additional materialis in a finely divided form and is dispersed in the carrier liquidseparate from the toner particles.
 32. A liquid toner according to claim20 wherein the polymer material comprises an ethylene terpolymer.
 33. Aliquid toner according to claim 20 wherein the polymer materialcomprises an ionomers.
 34. A liquid toner according to claim 20 whereinthe polymer material comprises an ethylene copolymer.
 35. A methodaccording to claim 20 wherein the additional material is at leastpartially incompatible with the toner particles.